The essence of the University of Arizona Superfund Basic Research Program (UA SBRP) renewal application is hazardous waste risk and remediation In the US Southwest. The theme of this Program Is to support development of a risk assessment process for metal and organic contaminants through toxicologic and hydrogeologic studies and innovative remediation technologies. Our application emphasizes hazardous waste issues in the Southwest (and Mexican Border) associated with the distinctive arid nature of the environment. Importantly, the outcomes of these studies can be extrapolated to arid environments around the world. Currently 1/3 of land surfaces are arid or semi arid and this proportion is expected to increase due to climate change. This is exemplified by the toxicants we study, metals (arsenic) and halogenated hydrocarbons, which are major contaminants in our region but also of significant concern throughout the world. Our Program consists of 9 research projects - five biomedical projects and four environmental sciences projects. Many of the projects are collaborative involving multiple disciplines. The biomedical projects are examining the mechanism of arsenic toxicity in target tissues, factors that affect the susceptibility of populations to arsenic-induced toxicity, and potential therapeutic approaches. The environmental sciences projects are investigating how hazardous wastes (arsenic, TCE/PCE) can be optimally characterized for risk assessment and remediation, and developing innovative techniques for assessing exposure and waste containment in our arid Southwest environment. These research projects are supported by five Cores that: administer the Program, translate the results to stakeholders, provide research services, promote unique outreach efforts to ethnic communities along the Border, and support graduate student training. This project will contribute to our understanding of toxicology and remediation of hazardous wastes nationally and internationally.